JP4311724B2 - Ultrasonic transducer array and ultrasonic transmitter / receiver - Google Patents

Description

  The present invention relates to an ultrasonic transmission / reception apparatus that transmits and receives ultrasonic waves in an ultrasonic imaging apparatus for medical use or structure flaw detection, and an ultrasonic transducer array used therefor.

  Conventionally, as ultrasonic transducers used for transmitting and receiving ultrasonic waves, piezoelectric ceramics such as PZT (lead zirconate titanate) and PVDF (polyvinyliden difluoride) are used. Piezoelectric elements including representative polymeric piezoelectric materials have been commonly used. When a voltage is applied to such a piezoelectric element via an electrode, the piezoelectric element expands and contracts due to the piezoelectric effect, and ultrasonic waves are generated. Therefore, an ultrasonic beam transmitted in a desired direction can be formed by arranging such a plurality of piezoelectric elements in one or two dimensions and driving each piezoelectric element with a predetermined delay. it can.

  FIG. 6 shows an ultrasonic transducer array used in a general ultrasonic probe. As shown in FIG. 6, a filler 102 that holds the ultrasonic transducers (elements) 101 is disposed between the plurality of ultrasonic transducers (elements) 101. In such an ultrasonic transducer array, when transmitting or receiving an ultrasonic wave, a plurality of adjacent elements interfere with each other acoustically, crosstalk occurs, and the SN ratio of the detection signal decreases. Has occurred. When the element 101 is expanded or contracted when transmitting or receiving ultrasonic waves, not only vibration for generating ultrasonic waves, but also horizontal vibration due to lateral expansion and contraction or undulation of the element itself, etc. This is because the vibration propagates to the adjacent element through the filler 102.

In order to solve such a problem, for example, a method of changing the shape and arrangement of the element can be considered. However, with the miniaturization and high integration of elements, it is difficult to manufacture elements having arbitrary shapes and to arbitrarily arrange such elements.
Or the method of optimizing the material of the filler arrange | positioned between several vibrator | oscillators is also considered. Non-Patent Document 1 describes an inter-element filling material in 1-3 composite (1-3 type composite piezoelectric material). For example, it is stated that polyurethane-based resins are soft and mechanically flexible and have good mechanical isolation. On the other hand, in the case of using a polyurethane-based resin, it is also stated that a problem remains to satisfy the condition that the composite material can be regarded as homogeneous as a piezoelectric vibrator. As described above, the material characteristics of the material that makes the element easy to vibrate in order to transmit ultrasonic waves having sufficient amplitude and the material that reduces crosstalk are contradictory to each other. Have difficulty.

Patent Document 1 discloses that an acoustic impedance is present between the transducer and the acoustic impedance of a living body on the surface of each transducer element of the narrow rectangular transducer elements arranged at equal intervals on the same plane. A single layer or a plurality of intermediate layer pieces made of a hard material, which is a value, are fixed, and the grooves between adjacent vibrators and intermediate layer pieces and the entire intermediate layer surface are covered with a soft resin. An array-type ultrasonic probe is disclosed. However, by setting the soft resin material in this way, it is possible to accelerate the convergence of the vibration propagating therethrough, but it is not possible to positively eliminate the vibration, so crosstalk between multiple elements can be avoided. It cannot be greatly reduced.
JP 54-131380 A Ultrasound Handbook, Maruzen Publishing (P.129-P.131)

  Therefore, in view of the above points, an object of the present invention is to reduce crosstalk between a plurality of elements in an ultrasonic transducer array in which a plurality of elements are arranged.

  In order to solve the above problems, an ultrasonic transducer array according to the present invention is disposed between a plurality of ultrasonic transducers that generate ultrasonic waves by expanding and contracting based on an applied voltage, and the plurality of ultrasonic transducers. A piezoelectric filling material, and at least one set of electrodes disposed on two opposing surfaces of the filling material.

  Further, an ultrasonic transmission / reception apparatus according to the present invention includes the above-described ultrasonic transducer array, and a drive unit that generates a plurality of drive signals for driving a plurality of ultrasonic transducers included in the ultrasonic transducer array, Voltage application means for applying a voltage to the filler via at least one pair of electrodes and the phase of the voltage output from the voltage application means are controlled so as to have an opposite phase to the vibration in the plurality of ultrasonic transducers And control means.

  According to the present invention, a filler containing a piezoelectric material is disposed between a plurality of ultrasonic transducers, and lateral vibration (mechanical energy) propagating through the filler is converted into electric energy and discharged through an electrode. Therefore, unnecessary vibration propagating through the filler can be positively eliminated, so that crosstalk between a plurality of ultrasonic transducers can be reduced, and the SN ratio in transmitting and receiving ultrasonic waves can be improved. become.

Hereinafter, the best mode for carrying out the present invention will be described in detail with reference to the drawings. The same constituent elements are denoted by the same reference numerals, and the description thereof is omitted.
FIG. 1 is a perspective view showing an ultrasonic transducer array according to the first embodiment of the present invention. The ultrasonic transducer array includes a plurality of ultrasonic transducers (hereinafter also referred to as “elements”) 10 arranged in two dimensions, a filler 11 arranged between and around the plurality of elements 10, and a filler. 11 and electrodes 12 and 13 disposed on the upper and lower surfaces. The ultrasonic transducer array is connected to an element driving unit 14 and a control unit 15 included in the ultrasonic transmission / reception apparatus main body. The element drive unit 14 includes a plurality of drive circuits respectively corresponding to the plurality of elements 10 and generates a plurality of drive signals for driving the plurality of elements 10. The control unit 15 controls the operation of the element driving unit 14.

  Each of the plurality of elements 10 is, for example, a minute columnar structure having a bottom surface width of about 0.2 to 1.0 mm and a height of about 1.0 mm. Each element 10 includes a piezoelectric material and electrodes formed at least at both ends thereof. When a voltage is applied to the piezoelectric material via these electrodes, the piezoelectric material expands and contracts due to the piezoelectric effect, so that ultrasonic waves are generated from the element. Each element 10 expands and contracts by receiving an ultrasonic wave propagating from the subject to generate an electrical signal (detection signal). As the piezoelectric material, a piezoelectric ceramic represented by PZT (lead zirconate titanate), a polymer piezoelectric material represented by PVDF (polyvinyliden difluoride), or the like is used.

  The filler 11 is made of PVDF (polyvinylidene fluoride), P (VDF / TrFE) (polyvinylidene fluoride trifluoride ethylene copolymer), P (VDF / TeFE) (polyvinylidene fluoride tetrafluoroethylene copolymer). ), P (VDCN / VAc) (vinylidene cyanide vinyl acetate copolymer), and a piezoelectric filling material containing a piezoelectric polymer such as PU (polyurea). As the filler 11, it is desirable to use a material having a large mechanical-piezoelectric conversion constant (piezoelectric output constant) g (V · m / N), that is, a material having high conversion efficiency. Here, the piezoelectric output constant g is expressed by (the intensity of the generated electric field) / (the applied stress).

  The electrodes 12 and 13 are arranged in a lattice shape so as to surround the periphery of the two end faces of the plurality of elements 10 on the upper surface and the lower surface of the filler 11. As shown in FIG. 1, the electrodes 12 and 13 are electrically connected to a reference potential. In this embodiment and the following embodiments, it is assumed that the reference potential is a ground potential. Hereinafter, the electrode disposed on the filler 11 is also referred to as a ground electrode.

  When transmitting an ultrasonic wave from the ultrasonic transducer array shown in FIG. 1, the element driving unit 14 drives the plurality of elements 10 by generating a driving signal under the control of the control unit 15. At that time, by driving each of the plurality of elements 10 with a predetermined delay time, an ultrasonic beam transmitted in a desired direction can be formed. On the other hand, when each element 10 expands and contracts, vibration (lateral vibration) generated from the element propagates to the filler 11 arranged around the element. As a result, the vibration (mechanical energy) of the filler 11 is converted into electric energy by the piezoelectric effect of the filler 11. As a result, the vibration converges and a voltage is generated between the electrode 12 and the electrode 13, and a current flows between these electrodes. As a result, vibration generated from a certain element is removed in the region of the electrodes 12 and 13 arranged around the element, and thus does not propagate to adjacent elements. Therefore, crosstalk between elements can be reduced.

  In the present embodiment, the electrodes 12 and 13 are discharged by being connected to the ground potential. However, the electrodes 12 and 13 may be short-circuited. Even with such a configuration, the vibration in the filler 11 can be converged.

  Next, an ultrasonic transducer array according to the second embodiment of the present invention will be described with reference to FIG. The ultrasonic transducer array according to the present embodiment includes a plurality of elements 10, a filler 11 formed of a piezoelectric filler material, and electrodes 12 and 13. The ultrasonic transducer array is connected to an element driving unit 14, a filler driving unit 20, and a control unit 21 included in the ultrasonic transmission / reception apparatus main body.

  The filler driving unit 20 is connected to the electrodes 12 and 13 and generates a voltage to be applied to the filler. The control unit 21 controls the operation of the element driving unit 14 and the operation of the filler driving unit 20.

  When transmitting an ultrasonic wave from the ultrasonic transducer array shown in FIG. 2, the element driving unit 14 generates a driving signal having a predetermined waveform under the control of the control unit 21. As a result, each element 10 expands and contracts to generate an ultrasonic wave, and lateral vibration propagates to the filler 11 disposed around the element. At that time, the filler driving unit 20 generates a voltage having a phase opposite to the waveform of the driving signal at a predetermined timing under the control of the control unit 21. Thereby, a voltage having an opposite phase to the drive signal is applied to the filler 11 via the electrodes 12 and 13. As a result, vibration occurs in the filler 11 based on the applied voltage, and the vibration and the lateral vibration propagated from the element cancel each other. Thereby, the lateral vibration generated from a certain element is removed in the region of the electrodes 12 and 13 arranged around the element, so that crosstalk between a plurality of elements can be reduced.

  In the first and second embodiments of the present invention described above, the filler driving unit is included in the main body of the ultrasonic transmission / reception apparatus. However, the filler driving unit together with the ultrasonic transducer array is used for ultrasonic waves. It may be provided in the probe.

  Next, an ultrasonic transducer array according to the third embodiment of the present invention will be described. FIG. 3A is a plan view showing an ultrasonic transducer array according to the third embodiment of the present invention, and FIG. 3B is a cross-sectional view thereof. The ultrasonic transducer array includes a plurality of elements 10 arranged in a two-dimensional matrix, a filler 11 formed of a piezoelectric filling material, and two of the plurality of elements 10 on the upper and lower surfaces of the filler 11. A plurality of sets of electrodes 31 and 32 arranged so as to surround each of the two end faces. On the upper surface and the lower surface of the filler 11, each of the plurality of opposing electrodes 31 and 32 is connected to a reference potential.

  As described above, in this embodiment, by providing a plurality of sets of grounding electrodes respectively corresponding to a plurality of elements, lateral vibration generated from each element is individually removed. Such a configuration is particularly effective in driving only a specific element or driving with a time difference between a plurality of elements when transmitting ultrasonic waves. Here, when the ground electrode is continuous on the upper surface or the lower surface of the filler, when a certain element (first element) vibrates, the ground electrode is caused by the piezoelectric effect of the filler disposed around the element. The whole becomes equipotential. As a result, the filler disposed around the second element, which is located away from the first element, results in the voltage being applied by the continuous grounding electrode, and the filler in that region vibrates and the second element is vibrated. 2 may be affected. However, as shown in FIG. 3, when the earthing electrode is arranged for each element, the voltage generated based on the lateral vibration propagated from a certain element is the earthing voltage arranged corresponding to the neighborhood. Since it is discharged individually by the electrodes, it does not affect the elements disposed far away.

  In this embodiment, a plurality of sets of electrodes provided corresponding to a plurality of elements are connected to a reference potential, but the electrodes may be short-circuited to each other in each of the plurality of sets of electrodes. Alternatively, as described in the second embodiment of the present invention, a drive circuit that generates a voltage having an opposite phase to the waveform of the drive signal of the element at a predetermined timing may be connected to each of the plurality of sets of electrodes. good.

Next, an ultrasonic transducer array according to the fourth embodiment of the present invention will be described. FIG. 4 is a diagram showing a part of the ultrasonic transducer array according to the present embodiment.
Similar to the ultrasonic transducer according to the third embodiment of the present invention, the ultrasonic transducer array according to the present embodiment includes a plurality of elements 10 and a filler 11 formed of a piezoelectric filler material. Yes. As shown in FIG. 4, a plurality of sets of electrodes 41 and 42 are disposed on the upper surface and the lower surface of the filler 11 so as to surround the periphery of the two end surfaces of the plurality of elements 10. Switch circuits 43 and 44 for switching electrical connection between the element 10 and the electrodes 41 and 42 are connected to the plurality of sets of electrodes 41 and 42, respectively. The switch circuits 43 and 44 are controlled by the control unit 40 so as to operate in synchronization with a drive signal supplied to drive the element 10. In the normal state (before driving the element), the connection between each of the electrodes 41 and 42 and the element 10 is off.

  When transmitting an ultrasonic wave from the ultrasonic transducer array and supplying a drive signal to the element 10, the element 10 expands and contracts to generate an ultrasonic wave, and lateral vibration propagates to the filler 11. Thereby, a voltage is generated between the electrode 41 and the electrode 42 by the piezoelectric effect of the filler 11. On the other hand, the switch circuits 43 and 44 are turned on after a predetermined timing from the generation of the drive signal. As a result, each of the electrodes 41 and 42 is connected to the element 10, and a voltage generated between the electrode 41 and the electrode 42 is fed back to the element 10. As a result, lateral vibration converges and energy loss in the element 10 is compensated.

Next, a desirable arrangement of the ground electrodes in the first to fourth embodiments described above will be described with reference to FIG. As shown in FIG. 5A, when the filler 11 is arranged around the element 10, the grounding electrode 50 is arranged at a position separated from the element 10 by a distance d that generally satisfies the following expression. It is desirable to do.
d = n × (λ / 4) (1)
Here, λ is the wavelength of the ultrasonic wave, and is given by λ = v / f using the sound velocity v and the vibration frequency f. In addition, n = 1, 2, 3,. For example, if the sound velocity v inside the living body is about 1580 m / s and the vibration frequency f is 15 MHz, the wavelength λ of the ultrasonic wave inside the living body is about 105 μm. Therefore, in this case, the ground electrode 50 may be disposed at a position of d = λ / 4 = 26.3 μm from the end of the element or an integer multiple of the position.

As shown in FIG. 5B, the amplitude of the lateral vibration generated from the element is maximized at a position that is λ / 4 from the end of the element 10 or an integral multiple thereof. Therefore, by arranging the grounding electrode at a position away from the element 10 by the distance d, the lateral vibration can be efficiently removed. In Formula (1), it is more preferable to use the effective value λ _e of the wavelength of vibration in the filler instead of the wavelength λ of the ultrasonic wave inside the living body.

  In the first to fourth embodiments described above, the grounding electrode may be short-circuited with the ultrasonic transducer on the upper surface or the lower surface of the filler. In that case, it is desirable to form an insulating layer on the surface of the ground electrode. For this purpose, for example, an insulating material such as glass may be formed on the surface of the ground electrode by sputtering, or an insulating material may be formed by oxidizing an electrode material such as nickel-aluminum, aluminum, or titanium.

It is a figure showing an ultrasonic transducer array concerning a 1st embodiment of the present invention. It is a figure which shows the ultrasonic transducer which concerns on the 2nd Embodiment of this invention. It is a figure which shows the ultrasonic transducer | vibrator which concerns on the 3rd Embodiment of this invention. It is a figure which shows a part of ultrasonic transducer | vibrator which concerns on the 4th Embodiment of this invention. In the 1st-4th embodiment of this invention, it is a figure for demonstrating the desirable arrangement | positioning of the electrode for earthing | grounding. It is a perspective view which shows the conventional ultrasonic transducer array.

Explanation of symbols

10, 101 Ultrasonic transducer (element)
11 Filling material (piezoelectric filling material)
12, 13, 31, 32, 41, 42, 50 Electrode (Earth electrode)
14 Element drive unit 15, 21, 40 Control unit 20 Filler drive unit 43, 44 Switch circuit 102 Filler

Claims (7)

A plurality of ultrasonic transducers that generate ultrasonic waves by expanding and contracting based on an applied voltage;
A piezoelectric filler disposed between the plurality of ultrasonic transducers;
At least one set of electrodes disposed on two opposing surfaces of the filler;
An ultrasonic transducer array comprising:   The ultrasonic transducer array according to claim 1, wherein the at least one set of electrodes is electrically connected to a ground potential.   The ultrasonic transducer array according to claim 1, wherein the at least one set of electrodes is short-circuited.   4. The device according to claim 1, wherein a plurality of electrodes are arranged so as to surround the periphery of two end surfaces of the plurality of ultrasonic transducers on two opposing surfaces of the filler, respectively. Ultrasonic transducer array.   On the two opposing surfaces of the filler, the at least one set of electrodes is disposed at a position that is an integral multiple of approximately ¼ of the oscillation wavelength of the ultrasonic waves from the ends of the plurality of ultrasonic transducers. The ultrasonic transducer array according to any one of claims 1 to 4.   A plurality of switchings that operate in synchronization with a drive signal for applying a voltage to the plurality of ultrasonic transducers and respectively switch connection states between the plurality of electrodes and two end faces of the plurality of ultrasonic transducers. The ultrasonic transducer array according to claim 4, further comprising means. The ultrasonic transducer array according to any one of claims 1 to 5,
Drive means for generating a plurality of drive signals for respectively driving a plurality of ultrasonic transducers included in the ultrasonic transducer array;
Voltage applying means for applying a voltage to the filler via the at least one set of electrodes so as to be in opposite phase to the vibration in the plurality of ultrasonic transducers;
Control means for controlling the phase of the voltage output from the voltage applying means;
An ultrasonic transmission / reception apparatus.

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